1. Field of the Invention
This invention relates to an improved rasp bar assembly for use in connection with threshing cylinders wherein several individual rasp bar sections may be mounted across a backing plate to permit the backing plate to flex at regions of discontinuity between the rasp bars. The invention also provides a novel rasp bar section which is configured to be carried by a backing plate in a manner to minimize failure caused by breakage thereof during threshing.
2. Description of the Prior Art
A number of different crops are harvested in a threshing process involving separation of the seed (grain) from the remainder of the plant by a combine which first cuts the plant and then separates the grain from the straw. After the plant is cut, it moves into the combine for contact with a rotatable threshing cylinder and a stationary concave mounted in opposition to the threshing cylinder. As the plant moves between the threshing cylinder and the concave, rasp bars mounted on the threshing cylinder rub or knock the grain from the heads. As used in this application, the threshing cylinders are defined as those mounting rasp bars and are used in conjunction with concaves.
The rasp bars are arranged across the width of the threshing cylinder and oriented perpendicular to the direction of rotation. FIGS. 1 and 2 of both U.S. Pat. Nos. 3,256,887 and 3,927,679 to Ausherman show generally a threshing cylinder with the rasp bars extending thereacross and an arrow indicating the direction of rotation of the threshing cylinder. Thus, the entire rasp bar engages the concave at the same time.
In the past, rasp bars have been made of hard materials such as ductile cast iron in order to wear well and thus be resistant to abrasion. Such rasp bars conventionally span the entire width of the threshing cylinder, and may be bolted to the threshing cylinder. Unfortunately, the hardness of the rasp bar is accompanied by brittleness of the same, which often results in breakage as the rasp bar is unable to flex when it encounters stones or other debris. Because the rasp bar is hard and unyielding, it breaks rather than bends. In use, it has been found that the rasp bars usually break at the bolt holes which mount the rasp bars to the threshing cylinder.
Consequently, there has developed a real need for a rasp bar assembly which combines the hardness of conventional rasp bar assemblies with a greater ability to flex and withstand impact and damage due to foreign objects entering the combine. In addition, there has developed a real need for a rasp bar assembly which provides for easy replacement of the rasp bars when worn, and allows for replacement of damaged or worn rasp bars at a minimum of expense. Finally, there has arisen a need for a rasp bar assembly for use with a concave which efficiently threshes the crop while minimizing stress to the rasp bars by minimizing the number of potential failure locations thereon.